In recent years, three-dimensional measurement has been applied extensively to various fields and hence many measurement methods, roughly categorized into contact scanning, non-contact active scanning, and non-contact passive scanning methods, have been developed. The contact scanning method uses a three-dimensional scanner to touch the surface of the object under test for calculating the outline depth of the surface of an object. For example, the coordinate measuring machine (CMM) is a typical contact three-dimensional scanner. In general, the measurement result of contact scanning is quite accurate, making it widely used in engineering and manufacturing industries. Nonetheless, the contact scanning method needs to contact the surface of an object during the scanning process and risking damaging the contact surface of the object under test by probes. Thereby, the contact scanning method is not suitable for the reconstruction of high-priced objects such as antiques or relics. Moreover, compared with other methods, contact scanning requires longer operation time; it cannot measure the surface of soft materials.
Non-contact active scanning means that measurement instruments need to emit light or electron beams to the surface of an object for three-dimensional measurement and acquiring three-dimensional information. The measurement instruments for three-dimensional information can calculate the three-dimensional space information by means of the light beams or energy reflected from the surface of an object. General measurement instrument adopt emitting light beams, such as visible light, infrared light, high-energy light beams, ultrasonic waves, and X rays, to the surface of an object. Nonetheless, the emitted energy or light beams in non-contact active scanning is usually influenced by the variations in the materials of the surface of an object, which induce multiple reflection or scattering and affect the reflected energy received by measurement instruments. Thereby, the measured information is erroneous. Besides, the emitted energy normally has its physical limitation, which influences the measured results. For example, infrared light emitted by various objects and human bodies is filled in the outdoor environment. Accordingly, the measurement instruments using infrared sensor are normally not used for the measurement in the outdoor environment.
The measurement instruments adopting non-contact passive scanning do not emit any energy or light beams. Instead, they receive the light reflect from the surface of an object under test, for example, the ambient light, for performing the measurement for three-dimensional information and achieving the expected effect. In a general environment, it is quite easy to acquire visible light for measurement. Thereby, most measurement instruments of non-contact passive scanning measure the visible light in the measurement environment. In most cases, the measurement instruments adopting non-contact passive scanning technology need no special hardware support. Hence, such kind of passive measurement products are very cheap. For example, the three-dimensional imaging system, namely, the 3D camera, is an important method of this type.
Traditional three-dimensional imaging systems adopt two cameras arranged in parallel and aimed at the object to be reconstructed for reconstructing three-dimensional shapes. In concept, this method is similar to human eyes, which deduce the depth of field of an image by matching the image content perceived from both eyes. If the distance between the two cameras and focal length are known and the image contents of the extracted left and right images can be matched successfully, the depth information of the scene recorded in the images can be calculated by triangulation. As shown in FIG. 1, an ideal binocular vision system is taken for example. The left image plane πl and the right image plane π, are coplanar. In the example, Ol and Or are the projection centers of the left and right cameras, respectively; pl, pr, ql, and qr are the projection points of the three-dimensional points P and Q to the left and right image planes, respectively. Assuming that (pl, qr) and (ql, pr) are the calculated corresponding point pairs, then P′ and Q′ as shown in the figure are given, resulting in erroneous correspondences. Thereby, the corresponding points of the left and right images relates to the correctness of the result. If errors occur in the corresponding points, the acquired three-dimensional location will be influenced by this erroneous correspondence.
Although the cost of equipment of the measurement method of non-contact passive scanning is cheaper than that of other measurement methods described above, the former usually requires multiple cameras for extracting images for measuring the environment depth as well as resolving the errors in the calculation of three-dimensional information due to errors in corresponding points.
Accordingly, the present invention provides a measurement system for three-dimensional information by rotating a single camera. In the present system, multiple images with different viewing angles are captured and used to calculate the feature points in the images. Then the disparity is calculated according to the feature point matching in a plurality of images. The disparity information, together with the parameters of the image extraction device, can be used to deduce the depth information of the scene. Thereby, the effect of a single camera can replace multiple cameras and wider environment depth information can be obtained.